Controlling means



Mal-'ch 28,1944. w s LANDO 2`,344,946

CONTROLLING MEA'NS FiledMarch- 26, 1941 2 Sheets-Sheet 1 Qkas %w n ATTORNEY March 28, 1944. I w s LANDoN 2,344,946

CONTROLLING MEANS Filed March 26, 1941 2 Sheets-Sheet 2 75 u, ATTORNEY Patenta! Mar. 28, 1944 PATENT orrcs coN'raoLNG MEANS Walter s. Landon, Detroit, Mieh., asslgnor to Detroit-Lubricator Company, Detroit, Mich., a cerporation of Michigan Application March 26, 1941, Srial No. 3853 11 Claims.

This invention relates to new and useful controlling means which among other uses is particularly useful in connection with an air supplying means for a fuel burning apparatus wherein it is adapted to function as a safety means in the event of failure of the required air supply.

One object of this invention is to provide a novel controlling means responsive tq failure of, or substantiai change in, operation of a driven 'or 'driving means.

Another object is to provide means by which such controlling means is rendered responsive to fluid flow.

Another object is to provide a novel safety switch for fluid Iuel bumers.

Another object is to provide a novel safety switch for actuation upon the failure of a sumcient air supply for a fluid fuel burner.

Another object is to provide a novel control in which a heated temperature responsive element is subject to a cooling eitect of a fluid to actuate a control means. e

, Another object is to provide a safety means which subsequent to operation indicative of an undesired condition, will maintain' itself in its operated position.

Another object is to provide asimple manuallyoperable means to reset the safety means.

These and other objects will be apparent from a reading of the speciflcation and claims.

The invention consists in the improved constructlon of and combination of parts. to be more Iully described hereinafter and the novelty of which will be' particularly pointed out and distinctly claimed.

In theaccompa nying drawings, to be taken as a part o! this specification, there are fully and clearly illustrated a number of the preferred embodiments of this invention, in which drawings- Figure 1 is a view showing a portion of air duct with -a control means embodying the invention positioned therein and showing one way inwhichthe control means may be connected into 'a burner control system;

Pig. 2 is a view showing a modified form of the control means;

m. 3 is a view. of another control means emv bodying the invention and attached to a 'fan u na; r

Pig. 4 is a view in section of the control means o! Flg. 3:

mg. 5 is a view in cross section of the housing which is secured to theyfan casing and showing' the air passageways through' the housing and mb sh the cum::

Fig. 6 is a view of the switch mechanism of the .control means of Fig; 3, and

Fig. 7 is a view of the control apparatus of Fig; 3 positioned with the temperature responsive 5 element located directly in an air duct.

Referring to the drawings by characters 'of reference, I designates generally an air duct through which air is caused to flow. In the embodiment as shown in Fig. 1, the duct I has a 10 threaded aperture therethrough in which is threadedly secured a nut-like supporting member 2 which is preierably made of "Bakelitef fiber or other insuating material and which carriea plate-like electrical conducting spring arms 3 and 4 extending into the duct I. The arms 3 and 4 carry at their free ends contact members 5 and 6 respectively. The innate resiliency of the arms-3 and 4 act to maintain the members 5 and 8 in engagement and in good electrical contact. Positoned between and extending substantially parallel with the arms 3 and 4 are plate-like electrica conducting spring arms 'l and 8 which have one end secured to and carried by the supporting member 2. The other or free ends of the arms 'I and 8 extend toward but not to the contact members 5 and 6 and have ofiset or rebent portions forming hooks 9 and o. The innate resiliency of the arms 'I and 8 acts to urge the arms 'I and 8 in a separating direction and to cause abutments ll and 12 to move into engagement with the arms 3 and 4 respectively. The force exerted by the arms 1 and 8 in a separating direction is greater than the force exerte'd by tthe arms 3 and 4 in urging the contact members 5 and 6 together so that upon engagement of the abutments il and l2 with the arms I and 4, the arms 3 and 4 will be moved in a separatlng direction and the contact members 5 and 8' will part thereby to open the circuit controlled 40 thereby. v

Normally the arms 'l and I are held against separating movement by a tusible member il which 'may be c-shaped as shown, or any other suitable form for hooking into the books 9 and n. The member i: is preferably of high resistance and is heated by an electrical current flowingtherethrough; Upon reaching: a predetermined temperature, the member I! will rupture thereby allowing the arms 'I and I to move apart and to open the circuit through the contact memv bers 5 and 6.* The circuit between the arms and s will also-be interrupted' by the ruptureof the fusible member !3. 4

The'numeral 4 desgnates .generaly a transui'ormerhavingaprimaryco ldecodthe arm 'I and thermostat 20.

or may be some manually operable switch or some other form o! control tor' an electric circuit. The other terminal of the thermostat 23 is connected by a lead wire 24 to the terminal ll of the transiormer 4 and to the arm 1. The arm is connected by a lead wire 20 to the lead wire 22 so that the member I: is connected directly across the supply. The motor diagrammatically shown at 20 and which may drive a !an tor forcing air through the duct l has one terminal connected to the lead wire 20 intermediate the arm 0 and wire 22 and has its other terminal connected by a lead wire 21 to the lead wire 24 intermediate g If desired, a switch 20 may be inserted in the wire 21 and automatically actuated in a manner to be hereinaiter described.

A lead wire 20 connects the terminal 20 ot the transtormer |4 to one terminal of an actuating means 00 which is shown in theiorm of 'a resistance and a lead wire :I connect the other terminalot the means00to thearmt. Thearm4 is connected by a lead wire 02 to the transtormer terminal |0 thereby completing the secondary circuit of the transtormer. The means 00 is adapted to actuate a iuel supply vave (not shown) and also is operable to actuate the switch 20. one method by which the means 00 might be operable to actuate a switch and valve is shown in my copending joint application-with Philip s.

Russel, Sertal No. 363367, filed October 29, 19-10,` tor Control apparatua cured within an aperture through the walls of a diagonally therefrom upward toward the member 40 to terminate in a hook portion 40 having a lip 40 which extends substantially paraliel to the portion 00. An insulating member 41 is suitably secured to the' lip 40 as by a rivet and has in the position of the parts as shown, a corner of the upper surface engaging the under surface oi' the bimetallic member 00. Normally, the upward i'orce exerted by the spring 44 is sufflcient to hold the parts against movement downward due to the force exerted by the blade member 40 and the bimetallic member 00. As the bimetallic member 00 increases in temperature, the member 00 increases its downwardforce flexing the lip 40 downward. This downward movement does not act to cause a parting ot the contact members 00 and 4i because as the contact member 05 is moved downward the inherent resiliency oi! the blade member 40 moves the contact member 4l downward with suflicient force to insure a good electrical contact between the members 30 and 4i.

As the temperature of the bimetallic member 00 reaches a predetermined temperature, the rotation of the bimetallic member 30 will, due to its radius arm about the post 01 and the bending ot the spring 44, slip over the edge oi' the member 41 and being relieved of the upward force exerted by the spring 44, the member u will snap or move with a quick movement to part the contact members 00 and 41; the blade member 40 being limited in its downward movement by engagement with the hook portion 40 oi' the spring 44. Subsequent to the partlng of the contact' plunger 40'is spherical and is adapted to engage the diagonally'extending portion of the spring 44.

' The outer or other end ot the plunger 40 projects duct I'. i The member 00 has integral therewith a supporting portion 00 extending inwardy into the duct land has' secured thereto, as by riveting, a current conducting post 01. A bimetallic strip member 00 which preferably has an appreciabie' resistance to current flow has one end secured to the top of the post 01 and extends there- !rom toward the supporting member 00 and through about one hai! the distance. The !ree end o! the member 00 has secured thereto and to its upper face a contact member 00. The supporting member 00 has securd thereto one end o! a strip spring blade member 40 which has its !ree end overlying the contact member 00 and threaded portion ot the member :I and extends rrom and is spaced. !rom the outer i'ac o! the supporting member 00 and has an annular head portion 40 suitably secured thereto as by screwthreading. A helicaly coiled compression spring 00 is positioned concentric with the plunger 40 and is under compression between the head portion 40 and supporting member 00 and acts to urge the plunger in an outward direction (toward the right as viewed in Fig. 2). Outward .novement ot the piunger is limited by an abutment !I which is rigid with the plunger 40 and which aigages 'the supporting member 00. Inward movement oi the plunger 40 causes the spherical end to against the spring 44 and flex it so that the lip 40 moves downward pushing the free end o! the bimetallic member 30 downward until the free end ot the member slides by the insulating member 41 and the contact members 00 and 4l then reengage. The plunger 40 is then released and spring 50 pushes the plunger 40 outward. until the abut-` ment Il engages the' supporting member 00.

Reterring to Figures 3, 4, 5 and 6 there is shown another form of switch generally designated 00. InFis.3theswitch00isshowncarriedbys housing 01 whichisintumsecuredto ataneasing 02. The casing 02 is of the scroll type and in which is positioned a pressure type tan 00 which is'held in place'therein and rotated therein by a .2`,s44,94e i 'suitable means such as an electric motor. 84.

Th casing 82 has an inlet (not shown) which opens axially into the central portion of the tan '83 and has an outlet 85 for connection to a duct for flow of air to the supplied means such as a fluid fuel burner. The casing 82 has a spiral side wall 68 -and substantially parallel end walls 8'! and 81 The wall 81 carries the motor 84 and the other wall !il has the inlet. The wall 88 has two apertures 88, -88 extending therethrough positioned midway between the end walls 81, 81' and spaced one from the other. e apertures 88 and 88 connect the housing 8! an casing 82 and form passageways for the flow of air therebetween.

The housing 8! is rectangular and hasside walls '!8, '!l, '!2 and 13 with the side Wall 88 of the' casing 82 forming one end wall. The other end of the housing 8! is closed -by the switch 88 and its cover '!4. The cover 14 is secured to the housing 8! by a suitable means such as a screw 14'. The side walls 18, '!l have passageways or apertures extending therethrough for the flow of air.

The switch 88 comprisesa substantially rectangular plate 'I'lpreferably of Bal relite" or other electrically insulating material having opposite substantially parallel surfaces '!8, '!9. A plurality of spacing members '!'I are carried by the plate '!1 and extend from the surface '!8 and have threaded apertures in their extended end portion for receiving screws '!'l which act to rigidly secure together the cover '!4 and plate '!1. Secured to the surface 18 is a bimetallic temperature sensitive means '!8 comprising a supporting member 88 and to which is secured one end of a .bimetallic strip 8!. The strip 8! is formed into a substantially circular portion 82 and has a lip portion 83 projectingsubstantially radially therefrom at the opposite end of the strip 82 from that which is secured to the member 88. An electric resistance heater unit 84 is positioned within and electriclosely flts the inside surface of the circular portion 82 so that there is a good thermal path therebetween. i The particular bimetallic shape and heater herein shown and described forms the subject matter of my co-pending application Serial No. 339, 127, filed June 8, 1940, for Heat actuated devices.

Adjacent one end of the plat '!1 and on the surface '!8 is a contact member 85 which 'i carried by one arni of an L-shaped current conducting plate member 88 which is secured to the surface '!9 as by a rivet'l. Held under the rivet 8'! and overlying the other arm of the member 88 is a terminal member 88 having a screw for a lead wire connection. A movable contact member 88 is secured to one end of a leaf spring 88 which extends toward 'the opposite end of th plate '!'I and along the surface 18. The end of the spring 88 opposite 'to the end having the contact member 89 is rigidly clamped between a rectangu'lar spacing block 8! which `is positioned against the surface 19 and the longarm of a T-shaped protecting member 82 which overlies the spring 88 and has its crossarms offsettoward the surface '!9. screws 83 extend through apertures in' the plate '!'I and clamp the oflset cross arms to the surface 18 and the supporting member 88 of the sensitive means, 18' to the surface 18. 4

A bell crank 84 has one ieg 88 secured to the spring 88 adjacent to but spaced from the block 9! and has its second eg 88 extending through `cally insulated from the circular portion 82 and an aperture in the plate '!'I and adjacent the bimetallic strip-lip portion 83. The heater unit 34 has its lead wi'es 81, 88. extending through apertures in the plate '!'I and along the surface 18. The lead wire 8'! is connected to the screw 83 which is adjacent the aperture through which it extends and is clamped thereto as by a nut. The lead wire 88 is secured to a terminal member 88 which is similar to the terminal member 88 and which has a screw for .attaching a lead wire thereto. The plate 1'! has an aperture !88 therethrough intermediate the screws 9.3 and positioned within the aperture !88 is a helical compression spring !8! which has one end engaging the supporting mem-ber 88 and has its other end engaging the ieg 95. The spring !8! normally acts to urge the ieg 88 against the end surface of the lip portion 83. I

As the temperature of the strip 8l increases, the lip portion 83 moves away from the surface '!8 and at a predetermined temperature the lip portion 83 will move beyond the end of the ieg 88 so that the spring !8l can act to rotate the bell crank 84 and to part the contact members 85 and 89 with a quick movement, thereby deenergizing the heater unit 84. Subsequent cooling of the strip 8! acts to cause the lip portion 83 to move toward the surface 18 but due to the' movement of the bell crank 94 by the spring !8! the arm 96 will be in the path of movement of the lip portion 83 and the portion 83 will be held from returning to the shown position. A resetting plunger !82 extends through an aperture in the T-shaped member 82 and is reciprocally guided therein, and has a head portion to prevent' Subsequent release of the plunger !82 will allow the-spring o to move the arm 88 against the end surface of the portion 83. Engagement of the arm 88 and end surface of the portion 83 will hold the contact members 85 and 88 in engagement.

In Fig. 7 the housing 8! has been omitted and -other respects the switch 88 is identical with the showing of the switch 88 in Figs. 3, 4 and 6.

The operation of the apparatus as illustrated in Fig. 1 is as follows: Upon closure of the circuit through the thermostat 23, our-rent flows through the lead wire 2 l, lead wire 24, arm 1, fuslble member !3, arm 8, lead wire 25 and lead wire 22. Closure of the circuit through the thermostat also acts to establish a circuit through lead wire 2!, lead wire 24 and lead wire 21 to the switch 28 which when closed completes the circuit to the motor 28 and to .the lead wire 25 which is connected to lead wire 22. At the time the thermostat 23 closes the circuits above mentioned, it also acts to energize the primary coil !8 of the transformer !4 which causes a current to flow through the secondary coil !8, lead wire 29, actuduct Air flowing through the duct flows over the fusible member !3 and acts to cause 'a rapid t e heating transfer of heat theretrom to the air stream. At the time the thermostat 23 established the current flow through the !usible member member I! began to heat up, due to its resistance to current flow, with the result that its temperature was caused to increase. The rate of increase in temperature of the member !3 is so related to the actuation oi the switch 20 by the means 30 that the temperature oi the member I! is not raisedto a point which will cause the member i: to rupture and part the contacts and 0 before the means :I actuates the motor !I to start air flow' through the duct I. If the ian driven by the motor !i acts to supply the desired air flow through the duet I, the rate o! heat transfer !rom the member I: to the air flowing through the duct I will be suiflciently great to prevent the heating eflect of the current flow through the member I: to raise the temperature ther-eo! to the point at which the member ruptures. irrespective o! the length oi' time the current flows through the !usible member II. The apparatu will then continue to function as described. Should. however, the air flow through the duct i i !all below a predetermined rate, the rate o! heat transfer from the member I! to the air within the duet I will diminish so that the temperature o! the member !3 will increase. causing the member to rupture. Rupture of the member II allows the arms l and I to fly apart and the abutments li and I! to engage and move the arms I and 4 respectively. in a parting direction to open' the secondary circuit o! the transiormer Il, thereby deenergising the means 30. Deenergization oi the means :I acts to -educe the iue flow to the heating apparatus (not shown) and to open the switch :e deenergizing the motor 20. The apperatus is' then in a safety position and the thermostat !I will be rendered ineflective to control the motor !I or means ll. To again place the appa ratus into operation, it is necessary to replace the member I l by a new one.

The operation ot the apparatus oi Fix. 2 is quite similar to that ot the apparatus of Fig. 1 but instead orusing a'rusible member I: this into operation etter the contact members msnually press inward on the head porto recloee the contact members 3! and the event the rate o! air or fluid flow the duet i' falls below a minimum rate, eflect of the current flowing through member s win increase the temperature cause the end carrying the contact to move downwardly against. the u until the corner oi' the movable end member I! slips over the corner of the insulanng member 41, at which time the. contact v the member u with the hook portion u. which occurs substantialy 'at the time the blde member u slides. oi! oi the insulating member II. 'nie member l'l is now in a posibere u and ll and cooling of the member !I will not cause the contact members !I and ll li have opened the circuit; it is necessary 'the portion IS enough to allow the contact member end o'r themember 3! to again slide by the member I'I and bring the member 39 into engagement with the member ll. Release oi the inward force manualiy exerted on the plunger u allows the spring II) to move the plunger ll tothe position shown.

In the modification as shown in Figs. 3-8, the circular portion o! e bimetallic strip li is heated by the heater t Il which has its circuit controlled by the contact members s and IS. Current is supplied by a lead wire (-not shown) to the terminal member 80, and then flows through the plate member 80, contactmembers 85 and u, spring se. member 92 to one lead wire !1 of the unit u, through the unit u, and through the other lead wire 90 of the unit u to the terminal member 99 which is connected by a lead wire (not shown) to complete the circuit. Air flow through the !an casing I! causes air to flow through the passageways II, u, 'Il and 'IS and over the strip Il, thereby increasing the rate of heat flow thereirom sufflciently to prevent the temperature thereot to raise sufliciently to cause the lip portion 83 to be moved beyond the end oi the leg !8 so that the spring ili is not eflective to part the contact members !5 and !9. Should the Ian 63 !aii to provide the desired air flow through the casing 62 the air flow over the strip 02 will be reduced sufllciently so that the temperature of the strip I! will increase and move the lip portion beyond the end o! the les OI, allowing the spring o to act to move the contact member 89 away !rom the contact member u. Parting or the contact members Il and .ll deenergizes the heater unit 84 and' allows the strip I! to cool. Movement o! the 'lip portion toward the position shown in Flgxlis limited, however, by engagement with the end surface o! the leg !i which will have been moved by the spring into thepath oi movement o! the lip portion 83. To reset the contact members II and I! in circuit making position. it is necessary to push in on the outer end surface of the plunger m which moves the leg Il oi' the beli crank u toward the suriace TI compressing the r spring ili and moving the leg I. out oi' the path o! movement of the lip portion !3. By the time the operatorgets around to Dushin: the piunger m, the strip !I will have cooled suflicienty so that the lip portionwill move substantialiy'to the position shown and 'upon release ot the plunger il! the lip portion u will hold the arm u as 4 shown and the contact member u in engagetion to prevent engagement oi the contact mem to reengage. 'ro reet the contact members u ment with the contact member ti.

The direction oi' flow of air through the passageways Bl, Il, ll and 'II will depend upon the restriction o! air flow through the outlet II. At high restrictions to flow through the outlet u. the air will flow !rom the casing .::and at low restrictions, the air flow will be into the casing fl. The apertures 'II and 'll maybe omitted entirely and, in this event, the air flow through the housing seems to be in through the passage-' way Il over the strip Il and out through the passageway ll. In each instance of operation. however, it has been ascertained that suflicient air flow is obtained to actuate the switch Il as desied. a

In'the showing oi' Fig. 7, the housing II has been eliminated and the strip Il placed directly intheairsteamflowingthroughtheduct IPto which the switch is secured. The operation substantialLv as previously described and will be readily apparent to those skilled in the art. I

It may now be seen 'that there is provided by this invention a simple means which is responsive not directly to' the temperature of the fluid in which the temperature sensitive element is placed but rather to the rate of fluid flow through a fluid conducting member. The means provided also acts to prevent further operation of the apparatus until the control has again been manually replacedgin operation. This apparatus, it will be apparent, is particularly adaptable for use when an abnormally low air or fluid flow 'would be highly objectionable or, as in a fluid fuel burner, dangerous.

What is claimedand is desired to be secured by Letters Patent of the United States is: i

1. In a switch-means of the character described, a piate-like insulating supporting member having substantially parallel opposite surfaces, a bimetallic temperature responsive member Secured to one of said surfaces and having a movable lip portion 'spaced from said one surface, a contact member carried adjacent the -of the switch under these circumstances is named contact member to control an electric circuitf said supporting member having an apertute therethrough and opening through said one surface and through said other surface adiacent said arm, means carried by said arm and having a portion overlying said other surface and having -a portion extending through said aperture a and engageable with the end surface of said lip other of said surfaces, a longitudinally extending flexible 'arm carried by and extending along said other surface, said flexible arm having one end portion held rigid with said supporting member and having its other end portion overiying said contact member, a second contact member carried by said arm other end portion and being` said other surface and having a portion extending through said aperture and engageable with the end surface of said lip portion, and means urging said arm in a direction to move said second contact member away frm said first-named contact member, said lip portion acting through said extending portion to hold said contact members in engagement against the force of said urging means, said responsive member acting upon a predetermined temperature thereof to move said lip portion out of engagem'ent with said extending portion thereby to allow said nrg ing means to move said second contact member out of engagement with said first-named contact member.

2. In a switch means of the 'character described, a plate-like insulating supporting member having substantialiy parallel opposite surfaces, a bimetallic temperature responsive member secured to one of said surfaces and having a movable lip portion spaced from' said one surface, electrical heater means positioned in heat exchange reiation with and operable to heat said responsive member, said responsive member beportion, and means urging said arm in a direction. to move said secondcontact member'away from said first-named contact member, said lip portion acting through said extending portion to hold said contact members in engagement against the force of said urging-means, said responsive member acting upon attainment of said predetermined temperature thereof to move said lip portion out of engagement with said extending portion thereby to allow said urging means to move said second contact member out of engagement with said first-named contact member.

3. In a switch means of the character described, a supporting member having opposite surfaces, a bimetallic temperature responsive member Secured to one' of said surfaces and having `a movable lip portion spaced from said one surface, a contact member carried adiacent the other'of said'surfaces, an arm carried by said other surface, said arm having one end portion held to said supporting member ,and having its other end portion overlying said contact menber, a second contact member carried by 'said arm other end portion and being cooperable with said first-named contact member to control an electric circuit, said supporting member having an aperture therethrough and opening through said one surface and through said other surface adjacent said arm, means carried by said arm and having a portion extending through said aperture and engageable with the end surface of said lip portion, and means urging said arm in a direction to move said second contact member. away from said first-named contact member. said lip portion acting through said extnding portion to hold said contact members in 'engagement against the force of said urging -means, said responsive member acting upon a predetermined temperature thereof to move said lip portion out of engagement with said extending portion thereby to allow said urging means to move said second contact member out of engagement with said first-named contact member.

4. In a switch means of the character de- 'scribed, a supporting member having opposite surfaces and having spaced apertures extending therethrough and" opening through said surfaces.

-a bimetallic temperature responsive' member having a movable lip portion, means securing said responsive member to one of said sui-faces and spacing said lip portion from said one surface, said securing.means having spaced apertures extending therethrough and aligned with ing operable to be cooled by fluid flow thereby to I maintain the temperature thereof below a predetermined temperature at fluid flows above a predetermined rate'of flow, a contact member carried adjacent the other of said surfaces, a longitudinally 'xtending flexible arm' carried by and 'extending -along said other surface, 'said flexible arm having one end portion held rigid with said supporting member and having its other end portion overlying said contact member, a second contact member carried by said armother end portion and being cooperable with said firstsaid supporting member spaced apertures, a contact member carried adjacent the' other of said surfaces, agrarm carried bysaid other surface, said arm having one end portion held to said supporting member and having its other' end portion a portion extending through said aperture and engageable with the end surface of said lip portion, a protecting member overlying at least a portion of said arm and having side flange portions, said flange portions having apertures therethrough aligned with said supporting member spaced apertures, means e'xtending through all oi said spaced apertures and acting to clamp together said securing means and said supporting member and said protecting member, said supporting member having a fourth aperture therethrough and registering with said securing means, and spring means positioned in said iourth aperture and seating against said securing means and said arm and urging said arm in a direction to move said second contact member away from said first-named contact member, said lip portion acting through said extending portion -to hold said contact members in engagement against the iorce oi said spring, said responsive member acting upon a predetermined temperature thereoi' to move said lip portion out oi' engagement with said extending portion thereby to allow said spring to move said second contact member out oi engagement with said firstnamed contact member.

5. In a switch means of the character described, a plate-like supporting member having opposite surtaces, a securing means having a surface seating against one o! said surfaces, a temperature responsive member carried by said means and having a movable portion spaced rrom said one surface. a first contact member carried adjacent the other ot said opposite suriaces, said supporting member having 'an aperture therethrough, a switch arm Iulcrumed to said-supporting member and extending' along and spaced !rom said other suriace and having a portion extending through said aperture !or engagement with said responsive member movable portion, a second contact member carried by said switch arm and oooperable with said first contact member to control an electric circuit upon movement of said arm, a protecting member overlying at least a portion of said switch arin, means clamping together said protecting member and said supporting member and said securing means, said supporting member having an aperture therethrough registering with said securing means, and meansspositioned in said aperture and held under stress intermediate said securing means and said switch arm said lastnamed means acting to urge said second contact member away from said first contact member and urging said switch arm portion into ngagement with,` said movable portion.

6. In a switch means of the character described, a supporting member having an aperture therethrough, a mounting bracket secured to one face oi' said member and overlying said aperture, a switch arm secured to said 'supporting member and overlying the other end of said aperture, a helical spring positioned in said aperture between said bracket and said arm and operable to actuate said arm, a bimetallic member carried by said bracket, a lever' arm 'extending from said switch arm and into abutting relation to said bimetallic member to hold said spring under compression, and an eiectric heating means !or said bimetallic member to warp said bimetallic member out of abutting relation to said lever arm so that said spring can actuate said switch arm.

7. In a safety switch to be oooled by heat transier to a fluid medium, a plate-like supporting member of eiectric insulating material, a temperature responsive looking element laterally movable upon temperature increase and mounted on one side of said supporting member, an eiectric heating coii directly carried by and bodiiy removable from said element and operable to heat said element, a switch member mounted on the other side of said supporting member, an Operating arm tor said switch member and extending into abutting relation to said element. said arm being locked by said element against switch member Operating movement, and means tending to move said arm !or switch member operation and-holding said arm against said element, said element moving out ot looking relation to said arm upon predetermined heating so that said tending means can move said arm.

8. In an apparatus oi the character described, a conduit for conveying air under pressure and having a side wall with an opening therethrough, a supporting plate member o! electric insulating material substantially closing said opening and forming a continuation oi the conduit side wall, a bracket on said plate member and extending into said conduit, a bimetal latch member carried by said bracket and positioned in said conduit ior cooling by air flow through said conduit, an eiectric heating element !or heating said bimetal member and supported in said conduit by said bimetal member, said plate member having an aperture therethrough. an eiectric switch mounted on said plate member external oi said conduit member and having a movable switch arm extending through said plate member aperture and into cooperable abutting latched engagement with said .bimetal member, and means stressing said arm toward switch opening position and urging said arm into' engagement with said bimetal member.

9. In an apparatus oi the character described. a. conduit !or conveying air under pressure and having a side wall with an opening therethroush, a pan-like housing secured to said wall and closing said opening and having its open side racing said opening, a supporting plate member of electric insulating material secured to and removable with said housing, said plate member substantially closing said opening and separating the interier of said housing :rom said conduit and -Iorming a continuation ot said side wall, a

bracket on said plate member and utending into said conduit, a bimetal latch member carried by said bracket and positioned in said conduit !or cooling by air flow through said conduit, an electric heating element for heating said bimetal member and supported in said conduit by said bimetal member, said plate member having an aperture therethrough, an eiectric switch mounted on said plate member external oi said conduit member and having a movable switch arm extending through said plate member aperture and into cooperable abutting latched engagement with said bimetal member, and means stres-;ing said arm toward switch opening position and urging said arm into engagement with said bimetal member.

10. A safety switch comprising a housing having a bottom wall and surrounding side walls. a supporting plate member of eiectric insulating material positioned in and extending across said housing 'parallel to said bottom wall to provide a switch compartment, a bimetal iateh member supported on said plate member external of said compartment, an eiectric switch carried by said plate member and positioned in said comlatch member, and an `e1ectric heating element carried by said bimetai latch member and operable to heat said latch member thereby -to flex said latch member out' of holding engagement with said switch arm so that said spring can actuate said switch. p

11. A safety switch comprising a supporting piate member of electric insulating material, a. supporting pad on said member, a. resilient switch blsde having one end fixed to said pad and extending substantially parallel to said plate member, a fixed switch contact on said plote member adjacent the free end ot said blade, a contact carried by said blade and cooperable with said fixed contact, said plate member having an aper-' ture therethrough, an angle lever having one arm fixed to said blade intermediate said secondnamed contact and said pad and having its other arm extending through said aperture. a bimetal latch member mounted on said plate member on the opposit'e side from said switch blade and having oneend in abutting engagement with said angie lever other arm; an electric heating element carried by andoperabie to heat said bi- .metal member thereby to flex said bimetal member out of abutting engagement with said lever other arm. and a spring acting on said lever one arm' and operabie to actuate said switch WAL'I'ER s. LANDON. 

